Try adding this code to .htaccess:
RedirectMatch 404 /\d{4}/\d{2}/\d{2}/(.*)\.html http://example.com/$1
It should fix the issue.
Try adding this code to .htaccess:
RedirectMatch 404 /\d{4}/\d{2}/\d{2}/(.*)\.html http://example.com/$1
It should fix the issue.